Nickel-chromium-cobalt alloy



Oct. 6, 1964 R. A. SMITH ETAL 3,151,981

NICKELCHROMIUMCOBALT ALLOY Filed Feb. 26, 1962 a Q B e a Z C 1N VEN 1CR5 6 01mm A. SMITH BY day/v f/sswp United States Patent 3,151,981NICKEL-QHROIVHUM- IOBALT ALLOY Ronald A. Smith, West Hagiey, and JohnHeslop, Sutton Coidfield, England, assi mors to The International NickelCompany, Inc, New York, N.Y., a corporation of Delaware Fiied Feb. 26,1962, Ser. No. 175,555 Ciaims priority, application Great Britain Feb.28, 1961 16 Claims. (Cl. 75-471) This invention relates to heatandcreep-resistant alloys and, more particularly, to nickel-chromium-cobaltalloys suitable for use in rotor discs for gas turbines.

The power rotors of gas turbines are subjected to the most severeoperating conditions of any part of the turbine and much eifort has beenexpended to ensure their satisfactory behavior. A common type of rotorconsists of a disc mounted on a shaft and carrying a number of bladesfastened to its rim by means of the well known fir-tree type of joint.Advances in the field of alloy evelopment during the last two decadeshave resulted in improved blading materials which have enabled operatingtemperatures, and hence turbine efliciency, to be greatly increased. Thematerials used for the disc components have not been correspondinglyimproved, partly owing to improvements in design, including thedevelopment of disc cooling techniques. However, operating conditionsare now such that many discs currently in use have no margin of safetyto allow for temperature overshooting due to failure of the cooling airsupply or other causes. Furthermore, with the marked increase inseverity of operating conditions accompanying the transition fromsubsonic to supersonic flight, a material with properties significantlybetter than those of the currently used alloys is essential.

The diiferent properties required of a rotor disc material are manifoldand complex and, to a large extent, conflicting. Of particularsignificance is the large variation of temperature occurring radiallybetween the center or hub and the periphery or rim of the disc. Thistemperature gradient is accompanied by a stress gradient in the oppositesense so that the highest stress occurs in the low temperature regionnear the hub and vice versa. A rotor disc material must, therefore, havea high creep strength, i.e., a low creep rate at high stresses, up torelatively high temperatures, e.g., 600 C., to ensure freedom fromdistortion by creep in service, particularly at the rim, and a highproof stress and ultimate tensile strength at more moderate temperaturesto ensure that the high hub stresses do not lead to distortion orfracture on loading. Preferably, the disc material should have a highvalue of Youngs modulus and a low coefiicient of thermal expansion tominimize the overall expansion of the disc. It must have adequateductility and must not be notch sensitive at temperatures correspondingto that at which the rim, with its fir-tree recesses, operates.Furthermore, the need to produce a relatively complex shape ofappreciable size requires that the alloy shall be hot workable.

It has now been discovered that by specially correlating alloyingredients, including nickel, chromium, cobalt, carbon, columbium(niobium), titanium, etc., an alloy especially suitable for use as gasturbine power rotor discs can be provided.

It is an object of the present invention to provide a novel alloy havingan advantageous combination of tensile characteristics, creepcharacteristics, ductility, thermal expansion characteristics, elasticcharacteristics, working characteristics, etc.

Another object of the invention is to provide a novel alloy especiallysuited for use as gas turbine structures, especially power rotor discs.

The invention also contemplates providing gas turbine power rotor discsmade of an alloy having an advantageous combination of tensilecharacteristics, creep characteristics and other characteristics,properties, etc., necessary to provide enhanced qualities of utility ina turbine power rotor.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the accompanying drawing in whichthe figure is a graph relating the percentage by weight of iron to thepercentage by weight of niobium in the present alloys.

According to the invention, the alloy contains, in percent by weight,about 0.03% to 0.09% carbon, about 14% to about 22% chromium, about 10%to 20% cobalt, from 3% to about 8% molybdenum, from 2% to about 3.5%titanium, from 0% to about 0.8% aluminum, the sum of the titanium andaluminum contents being greater than 2.5% (i.e., at least 2.6%), about2% to about 5.25% niobium (i.e., columbium), from 0% to about 25% iron,the contents of niobium and iron being so correlated that they arewithin the area ABCDEA in the accompanying drawing, about 0.001% to0.01% boron and about 0.01% to about 0.1% zirconium, the balance, apartfrom impurities and residual deoxidants, being nickel. The molybdenumcontent of the alloy can be up to about 10% (i.e., from 3% to 10%). Theusual major impurities in alloys of this kind are silicon and manganeseand not more than 1% of each of these may be present, and the totalamount of impurities and residual deoxidants should not exceed 2%. Theimpurity content should be kept as low as is practicable and, inparticular, it is advantageous to keep the silicon content below 0.3%.

It is important that the content of each of the constituents of thealloy should lie within the limits set out above.

Some carbon is necessary to ensure adequate ductility, but the carboncontent must be carefully controlled. If it is too low the alloy isunworkable, and at least 0.03%, and preferably at least 0.04%, should bepresent. As the carbon content increases the proof stress and tensileductility decrease, and for this reason the carbon content must notexceed 0.09%.

At chromium contents less than 14%, the resistance of the alloy tooxidation and to attack by the products of combustion of turbine fuelfalls off. On the other hand, increasing the chromium content tends toreduce the hot workability of the alloy. The chromium content must,therefore, not be greater than 22%. Cobalt has some beneficial effect oncreep resistance and also improves hot workability, and may usefully bepresent in amounts from 10% up to 20%. Molybdenum has a beneficialeffect on both tensile and creep ductility and is very desirable inorder to avoid notch sensitivity. On the other hand, excessive additionsof molybdenum carry the penalties of increased creep rate and decreasedmachineability and the content should, therefore, not exceed 10% and,advantageously, is not more than 8%. Molybduced. Aluminum has aparticularly harmful effect on ductility, and not more than 0.8% may bepresent. Other things being equal, lower levels of ductility areobtained in the presence of much iron than in its absence, and if theiron content exceeds 10%, the aluminum content preferably does notexceed 0.5% Increasing the titanium content also leads to a decrease inthe room temperature impact strength of the alloys, and the titaniumcontent must not exceed 3.5%.

The presence of titanium and niobium together within the ranges set outabove leads to a remarkable combination of strength and ductility, whileoutside these ranges there is a marked fall in one or both of theseproperties. If the niobium content is too low the creep rate at hightemperatures is too high, while excessive amounts of niobium havingregard to the iron content of the alloy lead to marked embrittlement ofthe alloys.

The best combination of properties, characteristics, etc., necessary forpractical utilization of the alloy in turbine parts, structures, rotors,etc., operating at temperatures from room temperature up to about 600 C.or higher, are obtained when iron is absent or present only as animpurity advantageously in amounts not exceeding about and the niobiumcontent is at the upper end of the range, that is, when the alloy isrepresented by a point lying within the area AFGEA in the accompanyingdrawing. As the iron content is increased, the niobium con tent must bedecreased, and it is an important feature of the invention that thecontents of these two elements are so related that they are within thearea ABCDEA in the accompanying drawing. Replacement of nickel by ironmakes the alloys cheaper, but also somewhat reduces their'tensilestrength and proof stress at high temperatures. The iron-containingalloys are, however, suitable for use where the operating conditions arenot extremely severe.

Niobium available from commercial sources is usually contaminated bytantalum, which element is substantially equivalent to niobiurn in itsefiect, and niobium may be partly or wholly replaced by an equal weightof tantalum up to a maximum tantalum content of 3%.

Small additions of boron and zirconium have markedly beneficial effectson tensile ductility at temperatures of 600 C. and above, and both ofthese elements must be present. However, as the content is increased themelting point of the alloys falls, and if more than 0.01% boron or 0.1%zirconium 'is present, serious deterioration in the hot workingproperties of the alloys results.

Advantageous compositions of iron free and iron containing alloys areset forth below:

The alloys can be air melted, but advantageously, they are melted andcast under vacuum conditions. If they are melted in air they areadvantageously deoxidized by means of magnesium. If too much deoxidantis added the workability of the alloys is seriously reduced and,advantageously, the residual magnesium content does not exceed 0.01%.Air melted alloys are advantageously refined by holding under vacuum inthe molten state for some time before casting. The pressure during thistreatment should not be more than 0.1 mm. Hg and advantageously islower, e.g., 5 microns or less. The temperature is suitably 1400"C.-1600 C., and the holding timeshould be at least 5 minutes and,advantageously, is at least 10 minutes. The cast ingots can be processedto rotor disc form by conventional extrusion, forging, or pressingtechniques.

The discs require suitable heat treatment in order to develop thecritical combination of properties required. The alloys are of theage-hardenable type and require both solution and aging treatments. Theformer is most important in that for a given alloy it largely decidesthe relative levels of creep strength and proof strength that can beachieved. Very high solution treatment temperatures give the highestpossible creep resistance, while on the other hand lower solutiontreatment temperatures favor increased proof strength. The solutionheating temperature should, of course, not be higher than the solidustemperature of the alloy, but high enough to ensure that allconstituents of the alloy are taken into solution. Subject to this, asuitable heat treatment for discs made from the alloys comprisessolution treatment for /2-8 hours at 900 C.-1200 0., followed by aircooling or oil quenching and then aging at temperatures in the range 600C.-850 C.

To eliminate the effects of residual cold work and to ensurereproducible mechanical properties the solution temperature isadvantageously at least 1000 C. and a high level of proof strengthtogether with reasonable creep strength is obtained after a heattreatment comprising solution heating for one hour at 1050 C., followedby air cooling and aging for 16-40 hours at 700 C. A further increase inproof stress is achieved by following the solution heating by a doubleaging treatment comprising heating for 2-4 hours at 750 C.-800 C., aircooling and heating for 16-40 hours at 680 C.-720 C., e.g., 700 C. Foriron-free alloys the solution heating temperature is advantageously atleast 1100 C.

By way of example, two alloys, Nos. 1 and 3, were made by vacuum meltingat a pressure of less than 1 micron Hg and cast under vacuum to ingotswhich were extruded to bar. The extruded bar was heat treated bysolution heating for one hour at 1000 C. followed by air cooling andaging at 700 C. for 16 hours and tensile and creep test pieces weremachined from it.

Two further alloys Nos. 1a and 3a, of similar composition to Nos. 1 and3 respectively, were air-melted and cast into 2 /2 inch diameter ingotswhich were forged to /2 inch diameter bar. The forging was completed ata temperature of about 800 C. to about 900 C. The forged bar was heattreated by solution heating for 1 hour at 1050 C., followed by aircooling and aging at 700 C. for 16 hours, and tensile and creep testpieces were machined from it.

Two additional alloys, Nos. 2 and 4, were air melted, and No. 4 was alsovacuum refined. Both were then cast into 7 inch square ingots that wereforged to round cheeses 2 inches thick and 18 inches diameter, theforging being completed at temperatures above about 1050 C. The cheeseswere solution heated for three hours at 1050 C. and air cooled.Specimens cut from the centers of the cheeses were aged by heating for16 hours at 700 C. (except where otherwise indicated), air cooled andmachined to form tensile and creep test pieces. The compositions of thesix alloys are given in Table I below and the results of tensile andcreep tests in Table II. The tensile tests are performed with aHounsfield tensometer:

TABLE I IComposition, percent by weight] Alloy Number Element 0. 06 0.04 0. 08 0. 09 0. 07 0. 06 18. 7 19. 2 20. 4 13.9 15.8 15. 9 14. 25 14.3 14. 4 13. 5 14. 5 13. 8 3. 95 4. O 3. 75 4. l 4. 9 4. 5 2. 65 2. 48 2.62 3. l 3. 55 2. 76 0. 73 0. 53 0. 52 0. 1 0. 32 0. 27 4. 5 5.10 4. 752. 4 2. 2 2. 36 0. 2 0. 2 0. 2 20. 3 19. 6 19. 7 0.005 0.004 0. 0040.005 0. 002 0.003 Zirconiunn 0.09 0. 06 0. 06 0. 03 0.03 0.02 Manganese0. 05 0. 05 0. 05 0. 05 0. 05 0.07 -'lic0n 0. 2 0. 3 0. l3 0. 2 0. 3 0.l3 Nickel Bal. Bal. Bal. Bal. Bal. Bal.

TABLE II Alloy No. Creep Properties 45 t.s.i./575 O No strain 0.05%strain No strain 0.05% strain in 338 in 197 in 230 in 275 hrs. hrs) hrs.hrs.

43 t.s.i./600 C- No strain in 150 hrs.

32 t.s.i./650 O 0.04%

strain in 170 hrs.

40 t.s.i./050 C Fracture 0.2% strain 02% strain in 750 in 1400 in 250hrs., hrs. hrs., fracfracture in ture in 1063 hrs., 1556 hrs.,elongation elongation 3.1%. 5.9%.

32 t.s.i./700 0.- Fracture in 95 hrs., elongation 21% Alloy N o. TensileProperties 0.1% PS (t.s.i.) 70 59 53 UTS (t.s.i.) 98 86 79 0EClongation, percent 21 25 0.1% PS (t.s.i.) 57 66 53 50 54 48 UTS(t.s.i.) 85 91 76 64 76 65 Elongation, percent 16 15 15 14 19 17 1 Agedfor 24 hours at 650 0.

PS =Proof stress.

UTS=U1timate tensile stress.

(t.s.i.) =long tons (2240 pounds) per square inch.

Elongations on gauge length 4X 4550i specimen.

The properties of further samples of alloys Nos. 2 and 4 cut from nearthe rims of the cheeses were similar to those given in Table II, exceptthat the tensile elongations were somewhat greater.

It will be observed that the proof stress and ultimate tensile stress ofthe alloys were higher in the form of forged bar than in the form ofextruded bar or forged rotor disc cheeses. This i due to the greateramount of Working performed at a fairly low temperature on the forgedbar. The extruded bar and forged cheeses were Worked at much highertemperatures and the material thus had much less residual cold Work. Inorder to form relatively large structures such as turbine rotor discs byforging, high working temperatures, e.g., greater than about 1050 C. arenecessary, and it is an important characteristic of the alloys that theyexhibit high proof strength and ultimate tensile stres even after suchtreatment.

The following tables show the effects upon the tensile propertiesdetermined by the Hounsfield tensometer at 600 C. or" varying thecontents of titanium, aluminum and niobium in some iron free and ironcontaining alloys. Impact strengths, Where given, were determined at 20C. The compositions given are all nominal. All the specimens were eithersolution heated at 1000 C. for 1 hour, air cooled, and aged at 700 C.for 16 hours (heat treatment A) or solution heated at 1050 C. for 1hour, air cooled, and aged at 700 C. for 16 hours (heat treatment B).

TABLE III Efiect of Varying Titanium Content (a) BASE COMPOSITION OFALLOY [Carbon 0.05%, chromium 20%, cobalt 14%, molybdenum 5%, aluminum0.4%, niobium 5%, iron 0%. boron 0.003%,

zirconium 0.03%, nickel balance. Specimens machined from forged bar(heat treatment B) Alloy No. Titanium, 0.1% P.S. U.I.S. Elongation,

percent (t.s.i.) (t.s.i.) percent (b) BASE COMPOSITION OF ALLOY [Carbon0.05%, chromium 15%, cobalt 14%, molybdenum 5%, aluminum 0.3%, niobium2%, iron 20%, boron 0.003%, zirconium 0.03%, nickel balance. Specimensmachined from extruded bar] Heat Elon- Notched Alloy treat- Ti, 0.1%P.S. U.I.S. gation, impact N o. ment percent (t .s.i.) (t.s.i.) percentstfrtenlgth,

All the alloys in Table III, except Nos. 5, 11 and 12, are in accordanceWith the invention. In Nos. 5, 11 and 12, the total titanium andaluminum content is less than 2.5% and a marked drop in tensile strengthand/or ductility (as indicated by percent elongation) is observed. Thevalues of the notched impact strength (Izod test) given in the lastcolumn show how this property is impaired as the titanium contentincreases.

TABLE IV Effect of Varying Aluminum Content BASE COMPOSITION OF ALLOY[Carbon 0.05%, chromium 20%, cobalt 14%, molybdenum Analyzed values.

The fall in ductility of alloy No. 18 (outside the present invention),in which the aluminum content is too high, compared with alloys Nos. 17and 1 (according to the invention) is very marked.

. 7 TABLE v Effect of Varying Niobium Content (a) BASE COMPOSITION OFALLOY [Carbon 0.05%, chromium 20%, cobalt 14%, molybdenum titanium 2.5%,aluminum 0.7%, iron boron 0.003%, zirconium 0.03%, nickel balance.Specimens machined from extruded bar (heat treatment B)] (b) BASECOMPOSITION OF ALLOY [Carbon 0.05%, chromium 15%, cobalt 14%, molybdenumtitanium 3.0%, aluminum 0.3%, iron 20%, boron 0.003%, zirconium 0.03%,nickel balance. Specimens machined from extruded bar (heat treatment B)]The decrcase'in tensile ductility and in impact strength shows how thealloys are embrittled when the niobium content is too high. Alloys Nos.1 and 22 through 24 are in accordance with the invention, Nos. 19, 20,21 and .25 are not.

As an illustration of the low creep strength (higher creep rate)exhibited by alloys in which the niobium content is too low havingregard to the iron content, the following creep properties were foundfor an alloy having the analyzed composition: C 0.06%, Cr 21.5%, C013.5%, Ti 2.05%, A1 0.25%, Mo 4.12%, B 0.006%, Zr 0.05%, Nb 2.42%, Fe0.2%, Si 0.3%, Mn 0.05%, Ni balance, after a heat-treatment comprisingsolution heating for 1 hour at 980 C. followed by air cooling and agingfor 24 hours at 750 C.

Test conditions Time to 0.2% total Life to Elongastrain fracture tionStress Temp. (hours) (hours) (percent) (t.s.i.) C.)

The results in TableVI demonstrate the need for some carbon in thealloys to make them forgeable and the way in which the proof stress andultimate tensile stress fall as the carbon content increases.

TABLE VI Base Composition of Alloy [Chromium 20%, cobalt 14%, molybdenum6%, titanium l Unlorgeable.

It is to be noted that the present invention provides alloys which for agiven iron content exhibit in the age- I 8 hardened condition aftersolution treatment, an optimum combination of engineeringcharacteristics when the given iron content is correlated to thecolumbium content in accordance with the accompanying drawing. Moreparticularly it provides such alloys which exhibit, after aheat-treatment suitable for forged gas turbine rotor discs, the highproof and tensile stress values together with high resistance todeformation by creep under high stresses at elevated temperatures, asevidenced by a low creep rate,

0 that are desirable for such parts. Design requirements for turbinestructures, in particular, gas turbine rotor discs, often dictate theuse of alloys having high proof stress, high ductility and moderatetemperature capability under creep conditions. In these circumstances,alloys containing 10% or more of iron together with correlated amountsof columbium within the range of 2% to about 4%, can economically beemployed. When design requirements indicate the use of alloys havingincreased temperature capability under creep conditions together with ahigh combined level of other engineering characteristics such as low andhigh temperature proof stress, ductility, tenacity, elasticity,expansivity, etc., alloys con-' taining less than 10% iron, for example,less than 5% iron, together with correlated amounts of columbium withinthe range of about 3% to about 5.25% can advantageously be employed.Thus, a particular advantage of the present invention lies in the factthat a range of alloys is provided having an optimum combination ofengineering characteristics for any particular design of structuressubjected in use to conditions similar to those under which gas turbinepower rotor discs are employed.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariation may be resorted to without departing from the spirit and scopeof the invention, as those skilled in the art will readily understand.Such modifications and variations are considered to be within thepurview and scope of the invention and appended claims.

We claim:

1. An alloy for use in turbine structures at temperatures up to about600 C. and higher consisting essentially in percent by Weight of about14% to about 22% chromium, about 10% to about 20% cobalt, about 3% toabout 10% molybdenum, greater than 2.5% total aluminum and titanium,said aluminum being up to about 0.8% and said titanium being at least 2%to about 3.5%, about 0.03% to 0.09% carbon, about 0.001 to about 0.01%boron, about 0.01% to about 0.1% zirconium, about.2% to about 5.25niobium correlated with up to about 25% iron with the balance beingessentially nickel, said alloy after solution treatment and agehardening exhibiting an optimum combination of high and low tem-'perature tensile characteristics, creep characteristics, ductilitycharacteristics and elastic characteristics for any particular ironcontent within said range of up to about 25 iron by virtue of the ironcontent being correlated to the niobium content so that the percentageof iron and the percentage of niobium are together representable by apoint lying within the area ABCDEA in the accompanying drawing.

2. An alloy as in claim 1 which contains less than 0.01% magnesium andless than about 0.3% silicon.

3. An alloy as in claim 1 which contains less than about 0.5% aluminumwhen the iron content exceeds about 10%.

4. An alloy as in claim 1 which is double aged after solution treatment.

5. An alloy for use in turbine structures at temperatures up to about600 C. and higher consisting essentially in percent by weight of about14% to about 22% chromium, about 10% to about 20% cobalt, about 3% toabout 10% molybdenum, greater than 2.5% total aluminum and titanium,said aluminum being up to about 0.8% and said titanium being at least 2%to about 3.5

about 0.03% to 0.09% carbon, about 0.001% to about 0.01% boron, about0.01% to about 0.1% zirconium, up to about 25% iron, at least one metalselected from the group consisting of tantalum in an amount up to 3% andnobium in an amount up to 5.25% with the total content of tantalum plusniobium being about 2% to about 5.25% and the balance essentiallynickel, said tantalum plus niobium being correlated with the ironcontent such that the correlation is represented by a point lying withinthe area ABCDEA in the accompanying drawing, whereby said alloy aftersolution treatment and age hardening exhibits an optimum combination ofhigh and low temperature tensile characteristics, creep characteristics,ductility characteristics and elastic characteristics at any particulariron content Within the said range of up to about 25% iron.

6. An alloy as set forth in claim 5 wherein the molybdenum is at leastpartially replaced by an equal atomic percentage of tungsten up to amaximum tungsten content of percent by weight.

7. An alloy as defined in claim 6 wherein the iron content is a maximumof about 10% and the niobium content is about 3 to about 5.25

8. A gas turbine power rotor disc made of the alloy of claim 6.

9. An alloy for use in turbine structures at temperatures up to about600 C. and higher, consisting essentially in percent by weight of about18% to about 22% chromium, about 13% to about 15% cobalt, about 4% toabout 6.5 molybdenum, about 2.25% to about 2.75% titanium, about 0.3% toabout 0.8% aluminum, about 0.04% to 0.09% carbon, about 0.001% to about0.01% boron, about 0.01% to about 0.1% Zirconium, about 4.5% to about 5%niobium, up to about 1% iron with the balance being essentially nickel.

10. A gas turbine power rotor disc made of the alloy of claim 9.

11. An alloy for use in turbine structures at temperatures up to about600 C. and higher consisting essentially in percent by weight of about14% to about 16% chromium, about 13% to about 15% cobalt, about 4% toabout 6.5% molybdenum, about 2.75% to about 3.25% titanium, up to about0.35% aluminum, about 0.04% to 10 0.09% carbon, about 0.001% to about0.01% boron, about 0.01% to about 0.1% zirconium, about 2% to about 2.5%niobium, about 18% to about 22% iron and the balance being essentiallynickel.

12. A gas turbine power rotor disc made of the alloy of claim 11.

13. An alloy for use in turbine structures at tempera tures up to about600 C. and higher consisting essentially in percent by weight of about14% to about 22% chromium, about 10% to about 20% cobalt, about 3% toabout 10% molybdenum, gerater than 2.5 total aluminum and titanium, saidaluminum being up to about 0.8% and said titanium being at least 2% toabout 3.5 about 0.03% to 0.09% carbon, about 0.001% to about 0.01%boron, about 0.01% to about 0.1% zirconium, about 3.5% to about 5.25%niobium correlated with up to about 5% iron with the balance beingessentially nickel, said alloy after solution treatment and agehardening exhibiting an optimum combination of high and low temperaturetensile characteristics, creep characteristics, ductilitycharacteristics and elastic characteristics for any particular ironcontent within said range of up to about 5% iron by virtue of the ironcontent being correlated to the niobium content so that the percentageof iron and the percentage of niobium are together representable by apoint lying within the area AFGEA in the accompanying drawing.

14. A gas turbine power rotor disc made of the alloy of claim 13.

15. An alloy as in claim 13 which contains less than 0.01% magnesium andless than about 0.3% silicon.

16. An alloy as in claim 13 which is double aged after solutiontreatment.

References Cited in the file of this patent UNITED STATES PATENTS2,920,956 Nisbet et al. Jan. 12, 1960 2,981,621 Thielemann Apr. 25, 19612,994,605 Gill et al. Aug. 1, 1961 FOREIGN PATENTS 710,413 Great BritainMar. 12, 1962

1. AN ALLOY FOR USE IN TURBINE STRUCTURES AT TEMPERATURES UP TO ABOUT600*C. AND HIGHER CONSISTING ESSENTIALLY IN PERCENT BY WEIGHT OF ABOUT14% TO ABOUT 22% CHROMIUM, ABOUT 10% TO ABOUT 20% COBALT, ABOUT 3% TOABOUT 10% MOLYBDENUM, GREATER THAN 2.5% TOTAL ALUMINUM AND TITANIUM,SAID ALUMINUM BEING UP TO ABOUT 0.8% AND SAID TITANIUM BEING AT LEAST 2%TO ABOUT 3.5%, ABOUT 0.03% TO 0.09% CARBON, ABOUT 0.01 TO ABOUT 0.01%BORON, ABOUT 0.01% TO ABOUT 0.1% ZIRCONIUM, ABOUT 2% TO ABOUT 5.25%NIOBIUM CORRELATED WITH UP TO ABOUT 25% IRON WITH THE BALANCE BEINGESSENTIALLY NICKEL, SAID ALLOY AFTER SOLUTION TREATMENT AND AGEHARDENING EXHIBITING AN OPTIMUM COMBINATION OF HIGH AND LOW TEMPERATURETENSILE CHARACTERISTICS, CREEP CHARACTERISTICS, DUCTILITYCHARACTERISTICS AND ELASTIC CHARACTERISTICS FOR ANY